The contribution of serum free light chain assay in the prognostic classification and monitoring of plasma cell disorders.

In 2001 reports began to appear of a new immunoassay to measure free immunoglobulin light chains (FLC) in serum, which provides much greater sensitivity than older methods such as immunofixation. The new FLC assay has enabled the detection of monoclonal protein that was previously undetectable in some patients with oligosecretory/ non-secretory myeloma and light chain amyloidosis (AL). FLC measurement by immunoassay provides quantitative results, correlating with disease activity, and constitutes an advance in the monitoring of light chain only myeloma, AL and non-secretory myeloma. Serum FLC concentration also reflects the disease course in the majority of patients with myeloma producing intact monoclonal immunoglobulin protein, and the measurement has been incorporated into the new response criteria. An abnormal κ/λ FLC ratio has been shown to be a risk factor for progression of monoclonal gammopathy of undetermined significance (MGUS), smoldering myeloma and solitary plasmatocytoma of bone. At the beginning of 2009 the International Myeloma Working Group (IMWG) published guidelines for serum FLC analysis in myeloma and related plasma cell disorders (PCD): First, in the context of screening, serum FLC assay in combination with serum protein electrophoresis and immunofixation yields high sensitivity and negates the need for 24-hour urine studies for diagnoses other than AL. Second, the baseline FLC measurement is of major prognostic value in virtually every type of PCD. Third, the FLC assay allows for quantitative monitoring of patients with oligosecretory PCD, including patients with AL and nearly 2/3 of those with non-secretory myeloma. [ABSTRACT FROM AUTHOR]